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Lexington class aircraft carrier
The Lexington class aircraft carriers are the first operational aircraft carriers in the United States Navy. (USS Langley (CV-1) was a strictly developmental ship.) There were three ships in the class: USS Lexington (CV-2), USS Saratoga (CV-3), and USS Constellation (CV-4). The Lexington-class carriers were constructed on hulls originally laid down as battlecruisers after World War I. But under the Washington Naval Treaty of 1922, all U.S. battleship and battlecruiser construction was cancelled. However, the Treaty allowed three of the unfinished ships to be converted to carriers. They proved extremely successful as carriers, supporting wide-scale operations. Experience with the Lexington class convinced the Navy of the value of large carriers. The Lexington class carriers were the largest aircraft carriers in the fleet until both USS Lafayette and Midway class aircraft carriers were completed. The class served in World War II, seeing action in many battles. Though Lexington was lost in the first carrier battle (Battle of the Coral Sea), but later salvaged and rebuilt; Lexington, Saratoga and Constellation served to the end of the war and continued their careers deeper into the Cold War. Developement The Lexington-class were originally designed as battlecruisers, with heavy guns, high speed, and moderate armor protection. The Navy laid down six ships of the class from 1916 to 1919. When the battlecruisers were cancelled under the Washington Naval Treaty of 1922, three of the unfinished ships were designated for completion as carriers. USS Lexington (CV-2), USS Saratoga (CV-3), and USS Constellation (CV-4) were selected since they were the most advanced of the six ships in construction. Conversion became a series of compromises and mixed blessings which would not have arisen had they been "specifically designed carriers" from the outset. On the plus side, the ships would have better anti-torpedo protection, larger magazines for aircraft bombs and, with the after elevator 28 feet (8.5 m) higher than otherwise, more room for aircraft landings. On the minus side, a converted battlecruiser would be .5 knots (0.93 km/h) slower than a specifically designed carrier, have 16 percent less hanger space, less emergency fuel and, with "narrower lines" aft, not as wide a runway for which to aim. Costs were similar. A brand-new aircraft carrier was estimated at $27.1 million. Conversion of a Lexington class was $22.4 million, not counting the $6.7 million already sunk into them. Added together, the figure rose to $28.1 million. The bottom line, with the signing of the treaty, was that any capital ships under construction by the five signatories (the United States, Great Britain, France, Italy and Japan) had to be canceled and scrapped. For battlecruisers, this encompassed the United States' Lexington class, Japan's Amagi class battlecruiser, and Great Britain's G3 battlecruisers. For the U.S. Navy, the choice seemed clear. If it scrapped all six Lexingtons in accordance with the treaty, it would throw away $13.4 million that could otherwise go toward aircraft carriers. The Navy opted for the latter course. The next challenge the Navy's Bureau of Construction and Repair faced was the tonnage cap set by the treaty. Carriers were to be no more than 27,000 tons. An exception, spearheaded by Assistant Secretary of the Navy Theodore Roosevelt Junior and added to the treaty, allowed capital ships under conversion to go up to 33,000 tons, an increase of 6000 tons. This would almost not be enough for a conversion without removing half the power plant, something the Navy General Board did not consider an option. Creative interpreting of a clause in the treaty allowed a potential way out of this situation. The clause (Chapter II, Part III, Section I, (d)) read: No retained capital ships or aircraft carriers shall be reconstructed except for the purpose of providing means of defense against air and submarine attack, and subject to the following rules: The Contracting Powers may, for that purpose, equip existing tonnage with bulge or blister or anti-air attack deck protection, providing the increase of displacement thus effected does not exceed 3,000 tons (3,048 metric tons) displacement for each ship. No alterations in side armor, in calibre, number or general type of mounting of main armament shall be permitted except::(1) in the case of France and Italy, which countries within the limits allowed for bulge may increase their armor protection and the calibre of the guns now carried on their existing capital ships so as not to exceed 16 inches (406 millimeters) and :(2) the British Empire shall be permitted to complete, in the case of the battlecruiser HMS Renown (1916) the alterations to armor that have already been commenced but temporarily suspended. Without this clause, conversion might not have been feasible. Estimates made in 1928 estimates for the three ships put Lexington at an actual tonnage of 35,689 tons, Saratoga at 35,544, and Constellation at 35,550 tons. On official lists, the number given was 33,000 tons, with the footnote, "number does not include weight allowance under Ch. 11, pt. 3, Sec. 1, art. (d) of Washington Treaty for providing means against air and submarine attack". This tonnage number was the one these ships carried for their entire careers. Description General description Their official displacement on commissioning was 33,000 long tons (34,000 t) (in accordance with the Washington Treaty). In reality both ships were well in excess of that and displaced 36,000 long tons (37,000 t) at standard load. At full load (with fuel, ammunition, aircraft, gasoline, and stores) they displaced 47,700 long tons (48,500 t). Aside from their great size, their two most innovative features were located at the foremost part of the ships. The first was the "hurricane bow," a configuration of carriers where the bow was sealed up to the flight deck; this turned out to be the most useful of the three possible configurations for a carrier's bow (the other two being an additional flying-off deck and an antiaircraft battery). The second was a relatively new kind of bow called the bulbous bow or Taylor bow, named after its inventor, Rear Admiral David W. Taylor, who served as Chief Constructor for the U.S. Navy's Bureau of Construction and Repair (C&R) during World War I. The result of a series of towing tests begun in 1910, this bow reduced water resistance by an average of six percent, supported the forecastle and reduced bending stress on the hull. At speeds of more than 25 knots, test results were highly favorable. A disadvantage was the formation of a heavy layer of water which would creep up along the outer plating of the forecastle at higher speeds. However, this tendency could be reduced to some degree by careful design of the frames. Taylor first introduced this bow, also known as a bulbous forefoot, in his design of the USS Delaware (BB-28), which entered service in 1910. With its use in the German passenger liner Bremen, the Taylor bow would eventually become used widely in passenger ships, warships, tankers and large cargo vessels. Also, since the Lexingtons were extremely long, narrow vessels with an increased risk of bending stresses and insufficient longitudinal strength in their hulls, a then-unorthodox approach was adapted to framing them. Traditionally, a series of transverse frames would be fitted together closely from the keel upwards. Instead of this approach, the Lexington''s used longitudinal framing, also known as the Isherwood system after British naval architect Sir Joseph Isherwood, who patented it. This process used large, widely spaced transverse frames in conjunction with light, closely spaced longitudinal members to lend a ship much greater longitudinal strength than in ships built in the traditional method. Ships build with longitudinal framing proved to be exceptionally durable. In one case, the longitudinally-built tanker ''F.D. Asche survived grounding on two reefs in the Bahamas in 1921 and was towed to New York for repairs despite having virtually her entire bottom ripped out. Divers investigating the Asche while it was grounded found that, apart from the bottom being gone, the hull structure remained intact and therefore worth salvage. In another instance, the superstructure of the longitudinally-built steamer Curaca was blown away entirely and the frame buckled by a dynamite explosion in Halifax (former city) harbor during World War I but the ship stayed afloat. Design The Lexington-class aircraft carriers set the pattern for future American carrier designs of very large and long ships with topside flight decks, starboard-side islands, and a high-volume hangar decks. The tall funnel directed smoke well away from the flight deck and avoided smoke-fouling problems common with other early carriers. These ships were given a 866.17-by-105.9-foot (264.0 by 32.3 m) teak flight deck. Their hangar had a clear height of 20 feet (6.1 m) and encompassed 33,528 square feet (3,114.9 m2). It was the largest enclosed space afloat, civilian or military, when built. The hangar was 424 feet (129.2 m) long and its width varied from 68 to 74 feet (20.7 to 22.6 m), constrained by the bulky funnel uptakes and boat compartments. The height of the hangar was not exceeded on an American aircraft carrier until the United States class aircraft carriers, and Forrestal class aircraft carriers appeared in the mid-1950s. Aircraft repair shops, 108-foot (32.9 m) long, were aft of the hangar and below them was a storage space for disassembled aircraft, 128 feet (39.0 m) long. The hangar was divided by a single fire curtain just forward of the aft aircraft elevator. The carriers were fitted with two hydraulically powered elevators on their centerline. The forward elevator was 30-by-60-foot (9.1 × 18.3 m) and had a capacity of 16,000 pounds (7,257.5 kg). A 20-by-26-foot (6.1 by 7.9 m) section of the flight deck adjoining the rear edge of the elevator could split down the centerline to lift aircraft otherwise too long. Carrying 12,000 pounds (5,400 kg), it moved at a speed of 2 feet per second (0.61 m/s). The aft elevator measured 30-by-36-foot (9.1 by 11.0 m) and could only lift 6,000 pounds (2,721.6 kg). Munitions were delivered from the magazines by two hydraulically powered bomb lifts and one torpedo lift. A folding crane with a capacity of 10 long tons (10 t) was positioned on the flight deck forward of the gun turrets. Aviation gasoline was stored in eight compartments of the torpedo protection system and their capacity has been quoted as either 132,264 US gallons (500,670 l; 110,133 imp gal) or 163,000 US gallons (620,000 l; 136,000 imp gal). A flywheel-powered aircraft catapult, 155 feet (47.2 m) long, was fitted at the bow; it could launch a 10,000-pound (4,536 kg) aircraft at a speed of 48 knots (89 km/h; 55 mph). It was removed in 1934 as unnecessary. Propulsion Turbo-electric propulsion had been selected for the battlecruisers and was retained when they were converted into aircraft carriers because American companies struggled to produce the very large geared turbines necessary for such big ships. One advantage of turbo-electric drive were that the substitution of flexible electric cables for bulky steam-lines, which allowed the motors to be mounted further to the rear of the ship; this reduced vibration and weight by shortening the propeller shafts. Another was the ability to go astern at full power without needing a separate reverse turbine to do so, simply by reversing the electrical polarity of the motors. Two more benefits were the facility to operate all four propellers even if one of the turbo generators failed, which eliminated loss of speed due to the drag of a non-rotating propeller, and the possibility of operating only some of the generators at low speed with suitably higher loading and greater efficiency. "drive was efficient, rugged and always reliable. But it was also heavy, intricate, and not easy to maintain and keep tuned up." It posed the danger of high voltage to the crew. The machinery also required special ventilation measures to dissipate heat and to keep out any salt air. Even with this and elaborate insulation measures, protection from moisture or from flooding due to battle damage or other causes remained problematic. Each propeller was 14 feet 9 inches (4.50 m) in diameter and each of the four propeller shafts was powered by two 22,500-shaft-horsepower (16,800 kW) electric motors acting in tandem. These motors were about five times the size of any earlier electric motor. Four General Electric turbo generators powered each propeller shaft and each was rated at 35,200 kilowatts (47,200 hp), 5000 volts and 4620 amps of direct current (DC). Each of the four AC alternators produced 40,000 KVA. Sixteen water-tube boilers, each in their own individual compartment, provided steam for the generators at a working pressure of 295 psi (2,034 kPa; 21 kgf/cm2) and a temperature of 460 °F (238 °C). The turbo-electric machinery of the Lexington-class ships was designed to produce a total of 180,000 shaft horsepower (130,000 kW) and propel the ships at 33.25 knots (61.58 km/h; 38.26 mph), but each ship reached over 202,000 shp (151,000 kW) and 34.5 knots (63.9 km/h; 39.7 mph) during sea trials in 1928. Six 750-kilowatt (1,010 hp) DC turbo generators were installed in the upper levels of the two main turbine compartments. The ships carried a maximum of 6,688 long tons (6,795 t) of fuel oil, but only 5,400 long tons (5,500 t) of that was usable as the rest had to be retained as ballast in the port fuel tanks to offset the weight of the island and main guns. They demonstrated a range of 9,910 nautical miles (18,350 km; 11,400 mi) at a speed of 10.7 knots (19.8 km/h; 12.3 mph) with 4,540 long tons (4,610 t) of oil. Armament The Navy's Bureau of Construction and Repair was not then convinced that aircraft could be an effective and sufficient armament for a warship. Thus the design as carriers included a substantial gun battery of eight 8-inch 55 caliber guns in four twin gun turrets. These turrets were mounted above the flight deck on the starboard side, two before the bridge, and two behind the funnel. The guns in theory could fire to both sides, but it is probable that if they were fired to port (across the deck) the blast would have damaged the flight deck. The guns could be depressed to −5° and elevated to +41°; they were loaded at an angle of +9°. They fired 260-pound (118 kg) projectiles at a muzzle velocity of 2,800 ft/s (850 m/s); this provided a maximum range of 31,860 yd (29,133 m) at maximum elevation. A 20-foot (6.1 m) rangefinder was fitted on top of the pilothouse to provide fire control for these guns. Their anti-aircraft armament consisted of twelve 25-caliber 5-inch guns which were mounted on single mounts, six on each side of the ship. They had a maximum elevation of 85°. They fired 53.85-pound (24.43 kg) projectiles at a muzzle velocity of 2,110 ft/s (640 m/s). Their maximum range against surface targets was 17,700 yd (16,200 m) at 30° elevation and they had an anti-aircraft ceiling of 27,400 yd (25,100 m) at 85° elevation. The experience of the "Fleet Problem" exercises of the 1930s showed that planes were sufficient and the guns were unnecessary. The guns were removed from both ships just after the attack on Pearl Harbor. (The removed guns were used as shore-defense guns in Hawaii.) The 8-inch gun turrets were to be replaced with dual 5" DP gun turrets (the standard mounting on U.S. battleships and cruisers). On Saratoga, which had been damaged and was under repair for several months, this was done, but Lexington was rushed back into action with quad 1.1" mounts. Lexington was sunk before receiving her intended 5" guns. Armament The waterline belt of the Lexington-class ships tapered 7–5 inches (178–127 mm) in thickness from top to bottom and angled 11° outwards at the top. This angle increased the armor's relative thickness to horizontal, close-range fire, albeit at the cost of reducing its relative height which increased the chance of plunging shellfire going over or under it. It covered the middle 530 feet (161.5 m) of the ships. Forward, the belt ended in a bulkhead that also tapered from seven to five inches in thickness. Aft, it terminated at a seven-inch bulkhead. This belt had a height of 9 feet 4 inches (2.8 m). The third deck over the ships' machinery and magazine was armored with two layers of Special treatment steel (STS) totaling 2 inches (51 mm) in thickness. The steering gear, however, was protected by two layers of STS that totaled 3 inches (76 mm) on the flat and 4.5 inches (114 mm) on the slope. The gun turrets were protected only against splinters with .75 inches (19 mm) of armor. The conning tower was 2–2.25 inches (51–57 mm) of STS, and it had a communications tube with two-inch sides ran from the conning tower down to the lower conning position on the third deck. The torpedo defense system of the Lexington-class ships consisted of three to six medium steel protective bulkheads that ranged from .375 to .75 inch (10 to 19 mm) in thickness. The spaces between them could be left empty or used as fuel tanks to absorb the detonation of a torpedo's warhead. World War II service Lexington, Saratoga, and Constellation were all attached to the Pacific Fleet when the war broke out. Lexington participated in several raids on Japanese bases, but was sunk in May 1942 at the Battle of the Coral Sea. Saratoga served in several battles in 1942 through 1944, and was twice torpedoed by Japanese submarines, but on each occasion reached port under her own power. In September 1944, she was relegated to training duties, but she returned to combat duty in 1945. She was disabled by Japanese bombers in February 1945, and in June returned to training duties and to transporting returning troops to the U.S. With the development of jet aircraft after the war, Saratoga became obsolete. Her hangar was large enough for jets, but her elevators were too small, so they were removed and replaced with larger. Cold War service Category:American aircraft carriers Category:Lexington class aircraft carrier